A cryptographic communication network (a key sharing network) configured with a plurality of nodes, which is connected to each other through a plurality of links and networked, has been known. Each node has a function of generating and sharing a random number with opposite nodes that are connected via links, as well as has a function of performing cryptographic communication over a link by using a random number as a cryptographic key (hereinafter referred to as “a link key”). Further, some of the nodes also have a function of generating a cryptographic key (hereinafter referred to as “an application key”) which is a random number independent of the links, as well as have a function of transmitting the generated application key to a different node via a link. An application in the key sharing network has a function of acquiring an application key from a node and, using the application key as a cryptographic key, performing cryptographic communication with another application. The cryptographic data communication at this time may be performed using a network (an application network) which is different from the key sharing network, such as the Internet. Meanwhile, applications and nodes may be configured in an integrated manner. Alternatively, applications and nodes may be configured as terminals independent of each other, and application keys may be transmitted and received among the application and nodes.
In a node, the function of generating a random number (a link key) and sharing it with opposite nodes that are connected through links may also be implemented using, for example, a technique which is commonly referred to as quantum cryptographic communication. In this case, a technique in which a random number (an application key) is generated in a node independently of a link and the generated random number is transmitted to another node via a link is sometimes referred to as quantum key distribution (QKD).
An application may want to acquire an application key from a node faster and more stably. Accordingly, a node has a need to provide an application key to an application faster and more stably without being affected by restrictions (low throughput, variation, and the like) in by the quantum cryptographic technique.